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Thursday, August 18, 2022

Standardization of HCl solution

Learn about the preparation and standardization of hydrochloric acid solution through a laboratory experiment or practical.

To prepare and standardize 0.1 N HCl using sodium carbonate as a primary standard.


Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.

Chemicals: LR grade concentrated hydrochloric acid (HCl), sodium carbonate, (Na2CO3), methyl orange indicator, etc.

Apparatus: Digital/analytical balance

Principle of standardization of HCl:

In the titration of hydrochloric acid against the solution of sodium carbonate, methyl orange (a weak base) which is yellow in the unionized form is used as an indicator.

Standardization of HClWhen a weak base is used to titrate a solution that is just slightly acidic the endpoint is also slightly acidic. The solution is slightly alkaline when a weak acid is titrated with a strong base because the salt formed is partially hydrolyzed.

The reaction of sodium carbonate with hydrochloric acid is given below:

Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
CO32-(aq) + 2H+(aq) → CO2(g) + H2O(l)

In the process of acid-base titration, the portion of acid becomes chemically equivalent to the quantity of base present. When a strong acid and a strong base are tested at the same time, the solution turns out to be neutral.

Preparation of 0.1 N HCl solution:

Pipette out accurately 08.50 ml of concentrated hydrochloric acid (HCl) and dilute in 500 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with distilled water.

Preparation of sodium carbonate standard solution:

The molecular weight of sodium carbonate is 106. Therefore, weigh accurately 0.53 gm of Na2CO3 and dissolve in 50 ml of distilled water in a volumetric flask, once it has completely dissolved, make up the volume to 100 ml.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take primary standard anhydrous sodium carbonate (Na2CO3) and dry it at 250°C for 4 hours in a Petri dish or crucible.
  • Once it is cool, weigh accurately 0.22 g sodium carbonate and pour it into a conical flask.
  • Pour in 50 ml of water and stir the mixture to dissolve.
  • Add 2-3 drops of methyl orange indicator.
  • Titrate the sample solution with the prepared HCl solution until the light pink color appears.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.

Observation table:

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

Calculations:

Calculate the normality of the HCl solution (N),

As follows:

N = A /0.053*B

Where
A - gram of Na2CO3 used,
B - used ml of HCl solution in titration.

Result:

The strength of the prepared hydrochloric acid (HCl) solution was found to be_____N.


Frequently Asked Question (FAQ):

Why methyl orange is used in the standardization of HCl with Na2CO3?

Methyl orange is a better indicator for the titration of hydrochloric acid with sodium carbonate since the endpoint of the reaction falls in the pH range of 3.0 to 4.4 which is the pH range of Methyl orange.

What is the purpose of standardizing HCl acid solution?

To determine the concentration of a prepared solution of HCl we perform the standardization. Standardization is the process of determining a solution's exact concentration (Molarity/Normality). We can also use standard NaOH to measure the molarity of a hydrochloric acid solution.

What primary standard is taken in HCl standardization?

Usually, sodium carbonate (Na2CO3) is used as the primary standard in the standardization of HCl, as it complies with all the requirements (properties) of the primary standard. It has a high molecular weight, high purity, is non-toxic, is easy to weigh, and is non-hygroscopic.



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